1. Field of the Invention
The present invention relates to a switching mechanism and an electric switch, and more particularly to a switching mechanism for a spring-reversal type of electric switch appropriate for use in electric power tools.
2. Related Arts
Spring-reversal type of electric switches are used in electric power tools for closing and opening their circuits in which heavy current flows. Such spring-reversal type of electric switches give a pleasing click feeling to users at the time of turning on and off, and the quick xe2x80x9conxe2x80x9d and xe2x80x9coffxe2x80x9d switching action is appropriate for closing and opening circuits in which heavy currents flow. Also, spring-reversal type of electric switches can be used commonly for AC and DC.
Spring-reversal type of electric switches, however are liable to allow their contacts to bounce at the time of turning on and off. Particularly at the time of turning xe2x80x9conxe2x80x9d a rush current flows, thereby making it easy for arcs to appear across confronting contacts as a result of bouncing. Thus, the contacts will be badly worn or deformed and accordingly the life of the electric switches will be shortened.
A conventional contact-making mechanism comprises a spring reversal mechanism, a push spring for producing a given strength of pressure and associated movable contacts. The contact-making mechanism, however, is liable to reduce drastically its contact pressure just prior to the reversing action, which is caused by the push spring. If the electric switch should be shaken at the instant of the contact pressure being reduced, arks are liable to appear with the result that the contacts are badly worn or deformed.
With a view to solve these problems of spring-reversal type of electric switches, DE19930558A1 proposes an improved contact-making mechanism, which is described below by referring to FIGS. 18 to 25.
The improved spring-reversal type of electric switch 1 comprises a housing 2, a base 3, a cover 4, stationary contacts 5 and associated terminals 6, a slide 7 and associated movable contacts 8 (see FIG. 19), an operating lever 9 for switching operation, a first spring 10 and associated contact detents 11a and 11b (see FIG. 21), a second spring 12, a slider 13 and compression springs 28 (see FIG. 19).
As seen from FIG. 18, the housing 2 has four stationary contacts 5 and associated terminals 6 fastened to its bottom, and electric wires are connected to the terminals 6.
The slide 7 has four movable contacts 8 and two compression springs 28 on its lower surface as seen from FIG. 19. As seen from FIG. 20, the slide 7 is put in the housing 2 with the movable contacts 8 confronting the stationary contacts 5.
A carrier 16 has openings 17 on its opposite end walls (see FIG. 18). The carrier 16 contains the second spring 12, and is movable on the slide 7. Two stoppers 19a and 19b and a guide 14 are fastened to the upper surface of the slide 7. The guide 14 takes the role of guiding the projections 15a and 15b of the slider 13 for engaging with the second spring 12.
The slide 7 along with the slider 13 can move between the switching xe2x80x9coffxe2x80x9d position in which the movable contacts 8 are apart from the stationary contacts 5 and the switching xe2x80x9conxe2x80x9d position in which the movable contacts 8 are in contact with the stationary contacts 5.
The second spring 12 is a compression spring, which can produce a counter force opposite to the direction in which the slide 7 moves on the way to the switching point, and can produce a force in the direction in which the slide 7 moves when the switching point has been traversed.
The first U-shaped spring 10 is a kind of compression spring, and the U-shaped spring 10 has two legs 20a and 20b, each having a ramp 21 projecting outward. The spring constant of the first spring 10 is so determined that the force produced at the switching point of the first spring 10 may be equal to the sum of the two compression springs 28 positioned behind the movable contacts 8.
The contact detents 11a and 11b are given in the form of ramps 22 projecting inward from the opposite longitudinal sides of the housing 2. Each ramp 22 is shaped asymmetric.
The first spring 10 works in cooperation with the detents 11a and 11b as follows: when the operating lever 9 is pushed and rotated about its pivot to drive the slide 7 for the switching-on position, the spring 10 is responsive to movement of the slide 7 for storing its resilient energy as a counter reaction until the point of critical compression (switching point) has been reached, at which point of critical compression the resistance to movement of the slide 7 is maximized. Then, the stored energy is suddenly released to jerk the slide 7 to the switching-on position.
The slider 13 is operatively connected to the operating lever 9 so that depression of the operating lever 9 may make the slider 13 withdraw, and that release of the operating lever 9 may make the slider 13 advance. The slider 13 has a third spring 24 contained in its chamber 27, and it has stoppers 18a, 18b and 25 formed on its front and rear sides respectively. The stoppers 18a, 18b are formed on the projections 15a and 15b. 
The projections 15a and 15b act on the opposite ends of the second spring 12 via the guides 14 of the slide 7, as seen from FIG. 20.
There is play left between the stoppers 18a, 18b of the slider 13 and the stoppers 19a, 19b of the slide 7, so that the slider 13 when pushed forward may travel the short distance of play before engaging with the second spring 12.
The electric switch 1 turns on and off as follows: first, the electric switch 1 is put in the switching xe2x80x9coffxe2x80x9d-position as shown in FIG. 22, and then, the operating lever 9 is depressed so that the slider 13 may act on the left end of the second spring 12 via the projection 15a to stretch the spring 12. After reducing the play the stopper 18 mates with the stopper 19a with the result that the slide 7 is displaced rightward for the switching xe2x80x9conxe2x80x9d-position.
The slow displacement continues until the switching point has been reached while overcoming the counter force of the first spring 10 with its opposite legs abutting the detents 11a, 11b. After traversing the switching point the energy stored in the first spring 10 and the second spring 12 are released instantly, thereby jerking the slide 7 rightward to the switching xe2x80x9conxe2x80x9d position as shown in FIG. 23. The movable contacts 8 mate with the stationary contacts 5, and then, the compression spring 28 is compressed (see FIG. 20).
If it is desired that the electric switch 1 turn off, the operating lever 9 is released to reset the slider 13 by the third spring 24 (see FIG. 20). In resetting the slider 13 the projection 15b acts on the right end of the second spring 12, stretching the second spring 12 after reducing the play. For the while the slide 7 remains still, keeping the movable contacts 8 and stationary contacts 5 mating together.
Thereafter the slide 7 moves a very short distance leftward by the force of the first spring 10 abutting the steep inclinations 29b of the ramps 22. The movable contacts 8, however, are kept still abutting on the stationary contacts 5 as the compression spring 28 is loosened. This position continues until the switching point has been reached (see FIG. 25).
After the switching point is traversed, the total energy stored in the first spring 10 and the second spring 12 is released to jerk the slide 7 leftward instantly, allowing the movable contacts 8 to leave the stationary contacts 5. Thus, the electric switch 1 turns xe2x80x9coffxe2x80x9d, as shown in FIG. 22.
The electric switch 1 uses the compression spring (first spring 10) to suppress the bouncing of the movable contacts off the stationary contacts. Specifically the movable contacts are so controlled that they may come to touch the stationary contacts slowly, and that they may leave the stationary contacts quickly. It is, therefore, most likely that the switching xe2x80x9conxe2x80x9d and xe2x80x9coffxe2x80x9d timing varies significantly with the quality of the spring 10 used and with the wearing of the ramps 22 of the detents 11a and 11b. Therefore, electric switches having the same switching characteristics can hardly be reproduced.
One object of the present invention is to provide a heavy-current, long-lived AC/DC switching mechanism which is free of bouncing at the time of turning on, and is capable of cutting off the flow of heavy electric current instantly at the time of turning off.
A switching mechanism in a spring-reversal type of electric switch comprising: a casing having stationary contacts mounted therein; an actuator having movable contacts to mate with the stationary contacts and springs to push the rear sides of the movable contacts; an operating lever rotatable about its pivot for switching operation; a plunger operatively connected to the operating lever; a rotatable reversal member for driving the actuator; a reversal coiled spring one end of which is connected to the reversal member and the other end of which is connected to the plunger, the reversal coiled spring being responsive to transition across its reversal point for reversing its resilient force in direction, thus making the movable contacts move toward the stationary contacts or leave apart therefrom when depressing or releasing the operating lever,
wherein the switching mechanism is so constructed that the actuator is allowed to move a predetermined distance before reaching the reversal point on the way to the switching xe2x80x9conxe2x80x9d position, thus reducing the distance to the switching xe2x80x9conxe2x80x9d position to travel the remaining distance instantly when the reversal member reverses, thereby making the movable contacts mate with the stationary contacts quickly. The distance to the switching xe2x80x9conxe2x80x9d position is reduced to be short enough to cause little or no bouncing even if the movable contacts travel the remaining distance quickly to abut on the stationary contacts.
Also, the switching mechanism is so constructed that the actuator is prevented from moving before the reversal point is reached, and that the actuator is released after the reversal point is reached, thereby making the movable contacts leave the stationary contacts quickly. The reversal coiled spring can store a repulsive energy of the quantity large enough to make the movable contacts leave the stationary contacts very quickly when the stored energy is released. Also, advantageously the compressed coiled spring prior to arrival at the reversal point applies a push of good strength to the movable contacts against the stationary contacts, thereby avoiding unstable mechanical and electric contact between the movable and stationary contacts, which would be caused if the contact pressure were decreased between the movable and stationary contacts.
The rotatable reversal member has a pinion equipped therewith whereas the actuator has a rack equipped therewith. With this arrangement rotation of the reversal member is converted to the horizontal linear movement.
The plunger has a projection formed thereon; the rotatable reversal member has a projection formed thereon. These projections are so arranged that the projection of the plunger is responsive to depression of the operating lever for pushing the projection of the rotatable reversal member, thereby making the reversal member rotate thus to move the actuator and hence, the movable contacts close to the stationary contacts while stressing the reversal coiled spring.
The forward end of the plunger has a difference in level via a gentle slope formed on its lower surface. A stopper having a hook formed thereon is biased upward by a stopper spring to keep the stopper abutting on the lower surface of the plunger. The actuator has a projection to be caught by the hook of the stopper. With this arrangement the actuator is locked by allowing the projection of the actuator to be caught by the hook of the stopper. While the stopper follows and climbs the lower surface of the forward end of the plunger the actuator is being unlocked by releasing the projection of the actuator from the hook of the stopper.
On the way to the switching xe2x80x9conxe2x80x9d position the stopper is raised, and the projection of the actuator climbs the hook of the raised stopper to be caught thereby, when the movable contacts abut on the stationary contacts, together put in locking condition.
The operating lever is released toward the switching xe2x80x9coffxe2x80x9d position to move the plunger, the gentle slope of the forward end of which still holds the hook of the stopper and the projection of the actuator in the locking condition for a while after the reversal point of the reversal spring is traversed. Upon further movement of the operating lever toward the switching xe2x80x9coffxe2x80x9d position the stopper follows the gentle slope of the forward end of the plunger to be lowered for unlocking and jerking the actuator, thus making the movable contacts leave the stationary contacts quickly.
An electric switch according to the present invention comprises: an operating lever rotatable about its pivot; a plunger operatively connected to the operating lever to move linearly in response to rotation of the operating lever; a reversal member operatively connected to the plunger; a pinion fixed to the lower surface of the reversal member; a spring combined with the reversal member, responsive to the linear movement of the plunger for storing its resilient force until a predetermined strength of resilient force has been reached, and for releasing the stored strength of resilient force to rotate the pinion of the reversal member; an actuator having movable contacts and having a rack to meet with the pinion for moving linearly in unison with rotation of the pinion; and a casing having stationary contacts on its opposite sides, whereby the movable contacts and stationary contacts are made to meet with each other in unison with reversal action of the reversal spring.
The rotational-and-linear mechanism stores a predetermined strength of driving force, reducing the frictional engagement of associated parts. This has the effect of avoiding the wearing of parts caused by friction, and hence extending the life of the electric switch.